[PATCH] kNFSd: Introduce CROSSMNT flag for knfsd

Now that we have working up-calls to userspace,
CROSSMNT makes sense.
If CROSSMNT is set for an export, and we too a
LOOKUP which crosses a mountpoint, we initiate an
upcall to find out if and how that filesystem
is exported.

fs/nfsd/export.c

@@ -475,8 +475,14 @@ exp_get_by_name(svc_client *clp, struct vfsmount *mnt, struct dentry *dentry,
 
 	exp = svc_export_lookup(&key, 0);
 	if (exp != NULL) 
-		if (cache_check(&svc_export_cache, &exp->h, reqp))
+		switch (cache_check(&svc_export_cache, &exp->h, reqp)) {
+		case 0: break;
+		case -EAGAIN:
+			exp = ERR_PTR(-EAGAIN);
+			break;
+		default:
 			exp = NULL;
+		}
 
 	return exp;
 }
@@ -918,6 +924,7 @@ struct flags {
 	{ NFSEXP_KERBEROS, { "kerberos", ""}},
 	{ NFSEXP_SUNSECURE, { "sunsecure", ""}},
 	{ NFSEXP_NOHIDE, {"nohide", ""}},
+	{ NFSEXP_CROSSMNT, {"crossmnt", ""}},
 	{ NFSEXP_NOSUBTREECHECK, {"no_subtree_check", ""}},
 	{ NFSEXP_NOAUTHNLM, {"insecure_locks", ""}},
 #ifdef MSNFS

fs/nfsd/vfs.c

@@ -133,6 +133,12 @@ nfsd_lookup(struct svc_rqst *rqstp, struct svc_fh *fhp, const char *name,
 
 			exp2 = exp_parent(exp->ex_client, mnt, dentry,
 					  &rqstp->rq_chandle);
+			if (IS_ERR(exp2)) {
+				err = PTR_ERR(exp2);
+				dput(dentry);
+				mntput(mnt);
+				goto out;
+			}
 			if (!exp2) {
 				dput(dentry);
 				dentry = dget(dparent);
@@ -157,9 +163,19 @@ nfsd_lookup(struct svc_rqst *rqstp, struct svc_fh *fhp, const char *name,
 			struct dentry *mounts = dget(dentry);
 			while (follow_down(&mnt,&mounts)&&d_mountpoint(mounts))
 				;
+
 			exp2 = exp_get_by_name(exp->ex_client, mnt, 
 					       mounts, &rqstp->rq_chandle);
-			if (exp2 && EX_NOHIDE(exp2)) {
+			if (IS_ERR(exp2)) {
+				err = PTR_ERR(exp2);
+				dput(mounts);
+				dput(dentry);
+				mntput(mnt);
+				goto out;
+			}
+			if (exp2 &&
+			    ((exp->ex_flags & NFSEXP_CROSSMNT)
+			     || EX_NOHIDE(exp2))) {
 				/* successfully crossed mount point */
 				exp_put(exp);
 				exp = exp2;

include/linux/nfsd/export.h

@@ -40,7 +40,8 @@
 #define	NFSEXP_NOAUTHNLM	0x0800		/* Don't authenticate NLM requests - just trust */
 #define NFSEXP_MSNFS		0x1000	/* do silly things that MS clients expect */
 #define NFSEXP_FSID		0x2000
-#define NFSEXP_ALLFLAGS		0x3FFF
+#define	NFSEXP_CROSSMNT		0x4000
+#define NFSEXP_ALLFLAGS		0x7FFF
 
 
 #ifdef __KERNEL__